Are there any tutorials, talks or presentations that discuss the use of EC2 or other cloud computing services to host GIS Servers? Has anyone had any experience in doing it with Amazon's EC2? How hard is it to setup? I know that ESRI has some versions of their server products focused especifically to EC2, has anyone had success in using them?

OpenGeo (stack built around GeoServer and PostGIS) have an AMI available and a quick intro to AWS. It worked well for me, with a little tweaking. It's fairly straightforward to get up and running and you can save your own AMI to Amazon S3 once the server's set up the way you want it. The Firefox add-ins for AWS are very handy for managing S3 and EC2 (s3 fox & elastic fox).

There was a very good webinar put on this topic that gave a case study. It only took them 7 hours to move their application to EC2. It sounded like they had a very successful experience. Here is a link to the slides:

During this webinar esri announced they are planning to offer a 60 trial version of ArcGIS Server on EC2. They made it sound like it was coming soon and this webinar was in late November, so I imagine we should see something on this soon from esri.